In a serializer-deserializer (SerDes) system, it is desirable to have the capability to check the quality of the received and recovered signal. This is useful for determining the system margin and for debugging purposes. A receiver eye scan is an important technique to achieve this purpose. For analog-based SerDes systems, there are typically two approaches for obtain eye scans. The first technique is commonly referred to as a “destructive eye scan.” In the destructive eye scan mode, the slicing threshold and sampling phase of the actual data slicer are changed to perform the eye scan. Since the sliced data during the destructive eye scan can be incorrect, this eye scan technique cannot be used for receiving real data traffic. However, the destructive eye scan technique does not require additional hardware.
Another eye scan technique is “non-destructive” in that it can be used while receiving real data traffic without introducing errors. The non-destructive eye scan technique requires one or more extra slicers that are dedicated to the purposes of eye scanning. The dedicated eye scan slicers use different slicing thresholds and sampling phases compared to the slicers in the actual data path. Since the non-destructive eye scan technique does not interrupt normal operation, it can be used even in the asynchronous system where clock data recovery (CDR) is required continuously.
An analog-to-digital converter (ADC)-based SerDes exhibits a performance and cost advantage at higher data rates or for higher loss systems where advanced equalization techniques using digital signal processing become necessary. Time-interleaved ADC is preferred due to the stringent resolution and timing requirements. In such time-interleaved systems, a non-destructive eye scan becomes prohibitively costly due to the number of additional ADCs that are needed for the eye scan function. A destructive eye scan for an ADC-based SerDes has a minimal implementation cost, but it typically is limited to only synchronous systems. Thus, it is desirable to develop a new eye scan technique for ADC-based receivers that is less costly and can be used in both synchronous and asynchronous systems.